Project Summary Clinical signs of Cushing's syndrome include growth of fat pads (collarbone, back of neck, face, trunk), excessive sweating, dilation of capillaries, thinning of the skin, muscle weakness, hirsutism, depression/anxiety, hypertension, osteoporosis, insulin resistance, hyperglycemia, heart disease and a range of other metabolic disturbances resulting in high morbidity. If inadequately controlled in its severe forms, Cushing's syndrome is associated with high mortality. The most common form of Cushing's syndrome is Cushing's disease due to microadenomas of pituitary corticotrophic cells that secrete excess ACTH. First-line therapy for Cushing's disease is transphenoidal surgery to remove the pituitary tumor. Medical therapy is required when surgery is delayed, contraindicated or unsuccessful. Adrenal enzyme inhibitors (metyrapone, ketoconazole) prevent the synthesis of cortisol and can rapidly improve symptoms. However, metyropone is associated with hirsuitism in women (because of the accumulation of androgenic steroids) and patients must be monitored carefully to avoid hypoadrenalism. Ketoconazole often requires progressively increasing dosage to maintain disease control but this is ultimately limited by the hepatotoxicity of the drug. In addition, it is a potent inhibitor of CYP3A4 resulting in multiple drug-interactions. The recently approved somatostatin agonist, pasireotide inhibits ACTH secretion but only 15-26% of patients in a Phase III trial achieved normalization of urinary free cortisol while 73% of patients experienced a hyperglycemia-related adverse event due to the compound's potent inhibition of insulin secretion. Therefore a significant unmet medical need exists for improved agents to treat Cushing's disease. Here we propose to develop a novel class of small molecule, oral drugs to prevent excessive adrenal stimulation by ACTH. These agents should normalize cortisol levels, without the excess production of adrenal androgens or hepatotoxicity found with currently available adrenal enzyme inhibitors. Design and screening of a focused chemical library resulted in a high hit rate (60%) and emerging structure activity relationships of a family of drug-like starting points for medicinal chemistry. Here we propose to use medicinal chemistry to explore this chemical series and establish necessary counter-screens in order to demonstrate feasibility of this approach. If successful, an expanded medicinal chemistry effort in Phase II will result in a novel drug candidate for the treatment of Cushing's disease ready for preclinical activities needed to begin clinical trials.